Currently, one of the main techniques used in the field of hydrogen production is the steam reforming of hydrocarbons, especially including methane (SMR, the acronym for Steam Methane Reforming). Other techniques such as auto-thermal reforming (ATR) and catalytic or non-catalytic partial oxidation (POX) may also be used depending on the type of raw material to be treated. Via the reforming reaction, hydrocarbons are converted into a gaseous mixture comprising hydrogen (H2) and carbon monoxide (CO) according to the following reactions CnHm+nH2O+heat→nCO+(n+m/2)H2 or CnHm+n/2O2→nCO+(m/2)H2 as a function of the technique used.
The gaseous mixture thus produced is then commonly sent to a shift reactor (Water gas shift reactor) so as to produce more H2 and to convert the CO into CO2 via the following exothermic reaction: CO+H2O→CO2+H2. The gas thus obtained, which is rich in CO2 and H2, is then generally sent to a pressure swing adsorption module for hydrogen, known as PSA H2 (PSA being the acronym for Pressure Swing Adsorption), which allows hydrogen to be produced in high purity (from 99 mol % to 99.9999 mol %).
The residue from the pressure swing adsorption module for hydrogen (also known as the off-gas from the pressure swing adsorption module for hydrogen or off-gas from the PSA) itself contains all the CO2, the vast majority of the unconverted CH4 and CO, nitrogen (N2), argon (Ar) and hydrogen, the amount of which depends on the yield of the hydrogen pressure swing adsorption module.
Most commonly, the residual gas, including the CO2 it contains, is used as fuel in the burners of the reforming oven. The heat is used in the context of a thermal integration of the overall unit and/or to export steam. The residual gas is then expelled to the air.
In the context of reducing CO2 emissions into the atmosphere, solutions have been developed to make it possible to recover as much CO2 as possible in gaseous mixtures such as residual gases.
It is known practice, for example, to treat the residual gas from the pressure swing adsorption module for hydrogen to extract the CO2 therefrom.
EP-A-0 341 879 describes, for example, a treatment of the residue from the pressure swing adsorption module for hydrogen using a pressure swing adsorption module for carbon dioxide (PSA CO2) and a cryogenic part.
WO-A-2006/054 008, for its part, treats the residue from the pressure swing adsorption module for hydrogen using a cryogenic step and membranes. This process makes it possible to produce a stream of pure CO2, a stream of uncondensables and a stream rich in H2.
It is also possible to treat the gaseous mixture obtained via a second shift reaction upstream of the pressure swing adsorption module for hydrogen. Thus, FR-A-2 939 785 describes the use of a pressure swing adsorption module for CO2 and a cryogenic step producing a stream of pure CO2 and a stream rich in H2 which is treated thereafter in the pressure swing adsorption module for hydrogen.
These various methods for recovering CO2 are complex and require expensive installations especially with several pressure swing adsorption modules. There is thus a need for a process and/or an installation for separating and recovering CO2 and H2 from a mixture.
WO-A-2006/097 703 and FR-A-2 877 939 describe a process according to the preamble of claim 1, in which the adsorption module separates the mixture upstream of a cryogenic separation step.